Question

The half-life of a radioactive material is one hour. What would be the time required for 99.9% completion?

• A. 5 hours
• B. 10 hours
• C. 2 hours
• D. 20 hours

Answer 1

The correct option is B 10 hours

A $\stackrel{t_{1/2}}{\to }A/2\stackrel{2t_{1/2}}{\to }A/4$...........

Time require for 75% completion ($A\to A/4$) = 2 $t_{1/2}$

Proceeding in the same way we know that the time required for the 99.9% completion = 10 $\times t_{1/2}$

$t_{99.9\%}=10\times t_{50\%}=10\times 1=10$ hours.
Option B is correct.